The present invention relates generally to aqueous coating compositions containing selected combinations of aqueous binders, flop effect pigments and encapsulated thermochromic liquid crystal pigments.
Flop effect pigments such as, for example, metallic aluminum or mica, produce an appearance condition within the coating wherein light is differentially reflected by the pigment. This can result in a varying color appearance based upon angle of viewing. For most effect pigments of this type, the flop is only a small matter of degree--a particular color flops to a lighter or darker shade. No major color change is normally exhibited.
Thermochromic liquid crystals are liquid crystals which react to changes in temperature by changing color. These liquid crystals generally comprise chiral nematic biphenyl compositions and ester derivatives of cholesterol and other sterols, which may be encapsulated by well-known techniques as exemplified by the disclosures of U.S. Pat. Nos. 2,800,457 and 3,341,466, both of which are incorporated by reference herein for all purposes. It has been found, however, that the use of these encapsulated thermochromic liquid crystals often results in a non-uniform color appearance.
It has now been surprisingly discovered that the combined use of the flop and encapsulated thermochromic liquid crystal effect pigments in certain aqueous binder systems results not only in an unexpected change in the color flop effect (a distinct color shift) but also in a more uniform color appearance from the liquid crystals.